'XamlBindings': undeclared identifier in C++/WinRT

Describe the bug I get the compiler error 'XamlBindings': undeclared identifier when using x:Bind in a ControlTemplate as part of a XAML document that isn’t in the root namespace with C++/WinRT.

Steps to reproduce the bug

1. Create a new C++/WinRT UWP app (with minimum version 17763)
2. Create a page that isn’t in the project’s root namespace (ex BlankApp1.Foo.MyPage)
3. Within that page, retemplate a control and use x:Bind in the template, for example

   <Button x:Name="myButton" Click="ClickHandler">
       <Button.Template>
           <ControlTemplate TargetType="Button">
               <ContentPresenter Width="{x:Bind Width}" ></ContentPresenter>
           </ControlTemplate>
       </Button.Template>
       Click Me
   </Button>
   

4. Try building the project.
5. Observe a compiler error in Foo.MyPage.xaml.g.hpp

Expected behavior It builds.

Version Info Visual Studio 16.6.0 Preview 6.

NuGet package version: C++/WinRT 2.0.200508.4

Windows 10 version	Saw the problem?
Insider Build (19041)	Yes
November 2019 Update (18363)
May 2019 Update (18362)
October 2018 Update (17763)
April 2018 Update (17134)
Fall Creators Update (16299)
Creators Update (15063)

Device form factor	Saw the problem?
Desktop	Yes
Mobile
Xbox
Surface Hub
IoT

Additional context Full output:

1>------ Build started: Project: BlankApp2, Configuration: Debug Win32 ------
1>App.cpp
1>Foo.MainPage.cpp
1>XamlTypeInfo.g.cpp
1>T:\Projects\BlankApp2\Generated Files\Foo.MainPage.xaml.g.hpp(81,55): error C2065: 'XamlBindings': undeclared identifier
1>T:\Projects\BlankApp2\Generated Files\Foo.MainPage.xaml.g.hpp(71): message : while compiling class template member function 'winrt::Windows::UI::Xaml::Markup::IComponentConnector winrt::BlankApp2::Foo::implementation::MainPageT<winrt::BlankApp2::Foo::implementation::MainPage>::GetBindingConnector(int32_t,const winrt::implements<D,winrt::BlankApp2::Foo::MainPage,winrt::composing,winrt::Windows::UI::Xaml::Controls::IPageOverrides,winrt::Windows::UI::Xaml::Controls::IControlOverrides,winrt::Windows::UI::Xaml::Controls::IControlOverrides6,winrt::Windows::UI::Xaml::IFrameworkElementOverrides,winrt::Windows::UI::Xaml::IFrameworkElementOverrides2,winrt::Windows::UI::Xaml::IUIElementOverrides,winrt::Windows::UI::Xaml::IUIElementOverrides7,winrt::Windows::UI::Xaml::IUIElementOverrides8,winrt::Windows::UI::Xaml::IUIElementOverrides9,winrt::Windows::UI::Xaml::Markup::IComponentConnector,winrt::Windows::UI::Xaml::Markup::IComponentConnector2>::IInspectable &)'
1>        with
1>        [
1>            D=winrt::BlankApp2::Foo::implementation::MainPage
1>        ]
1>T:\Projects\BlankApp2\Generated Files\winrt\Windows.UI.Xaml.Markup.h(361): message : see reference to function template instantiation 'winrt::Windows::UI::Xaml::Markup::IComponentConnector winrt::BlankApp2::Foo::implementation::MainPageT<winrt::BlankApp2::Foo::implementation::MainPage>::GetBindingConnector(int32_t,const winrt::implements<D,winrt::BlankApp2::Foo::MainPage,winrt::composing,winrt::Windows::UI::Xaml::Controls::IPageOverrides,winrt::Windows::UI::Xaml::Controls::IControlOverrides,winrt::Windows::UI::Xaml::Controls::IControlOverrides6,winrt::Windows::UI::Xaml::IFrameworkElementOverrides,winrt::Windows::UI::Xaml::IFrameworkElementOverrides2,winrt::Windows::UI::Xaml::IUIElementOverrides,winrt::Windows::UI::Xaml::IUIElementOverrides7,winrt::Windows::UI::Xaml::IUIElementOverrides8,winrt::Windows::UI::Xaml::IUIElementOverrides9,winrt::Windows::UI::Xaml::Markup::IComponentConnector,winrt::Windows::UI::Xaml::Markup::IComponentConnector2>::IInspectable &)' being compiled
1>        with
1>        [
1>            D=winrt::BlankApp2::Foo::implementation::MainPage
1>        ]
1>T:\Projects\BlankApp2\Foo.MainPage.h(8): message : see reference to class template instantiation 'winrt::BlankApp2::Foo::implementation::MainPageT<winrt::BlankApp2::Foo::implementation::MainPage>' being compiled
1>T:\Projects\BlankApp2\Generated Files\Foo.MainPage.xaml.g.hpp(81,45): error C2672: 'winrt::make_self': no matching overloaded function found
1>T:\Projects\BlankApp2\Generated Files\Foo.MainPage.xaml.g.hpp(88,1): error C2974: 'winrt::make_self': invalid template argument for 'D', type expected
1>T:\Projects\BlankApp2\Generated Files\winrt\base.h(7458): message : see declaration of 'winrt::make_self'
1>Done building project "BlankApp2.vcxproj" -- FAILED.
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

This also affects other use cases, like a control inheriting from another and retemplating the parent, binding some values to its own properties. (that was how I found it, because my controls are under the MyRootNamespace.Controls namespace)

I cannot use TemplateBinding because I would like to provide a TargetNullValue fallback, which is not possible with TemplateBinding.

You can find my use case here https://github.com/TranslucentTB/TranslucentTB/tree/develop. The issue can be reproduced simply by building the Xaml project which has no other dependencies than the community toolkit’s XamlApplication, C++/WinRT and the VCTRForwarders.

Moved from https://github.com/microsoft/cppwinrt/issues/614

[RealTommyKlein]

We’ll also backport both fixes for Windows.UI.Xaml, but to set expectations for a timeline, it won’t be available until the Windows SDK release in mid-2021 due to the Windows shipping schedule.

[sylveon]

Would love to see this backported to the system XAML compiler, since I use XAML Islands so I would have to wait for WinUI 3.1 to get the fix